Flexible display panel

Abstract

The application provides a flexible display panel. The flexible display panel comprises a first organic substrate, a charge passivation layer, a first inorganic layer and a thin film transistor layer. The charge passivation layer is arranged on one side of the first organic substrate, and the charge passivation layer comprises an electron-accepting group. The first inorganic layer is arranged on the side of the charge passivation layer away from the first organic substrate. The thin film transistor layer is arranged on the side of the first inorganic layer away from the first organic substrate. The flexible display panel of the application can prevent the charges generated by polarization of the first organic substrate from affecting the thin film transistor arranged thereon, maintain the electrical stability of the thin film transistor and reduce the occurrence of residual images.

Description

TECHNICAL FIELD

[0001] The present application relates to the display technical field, and in particular to a flexible display panel. BACKGROUND

[0002] With the rapid development of modern display technology, the display technology field is developing towards the direction of being lighter, thinner, more flexible and more transparent. Traditional glass substrates are difficult to meet the requirements of future flexible display technology due to their own characteristics such as hardness and brittleness. The polymer thin film substrate has the characteristics of light weight and high mechanical strength, and at the same time, based on the requirement of flexibility of the display panel, the flexible polymer thin film substrate is the preferred material for future flexible display technology.

[0003] However, it is found in actual application that the display panel with an organic flexible polymer material as the substrate is more prone to image sticking than the display panel with glass as the substrate. SUMMARY

[0004] Therefore, the present application provides a flexible display panel capable of reducing image sticking.

[0005] The present application provides a flexible display panel, which comprises:

[0006] a first organic substrate;

[0007] a charge passivation layer disposed on one side of the first organic substrate, the charge passivation layer comprising an electron-accepting group;

[0008] a first inorganic layer disposed on the side of the charge passivation layer away from the first organic substrate;

[0009] a thin film transistor layer disposed on the side of the first inorganic layer away from the first organic substrate.

[0010] Optionally, in an embodiment, the charge passivation layer is disposed on the surface of the side of the first organic substrate close to the thin film transistor layer.

[0011] Optionally, in an embodiment, the flexible display panel further comprises:

[0012] a second inorganic layer disposed between the first organic substrate and the first inorganic layer;

[0013] a second organic substrate disposed between the second inorganic layer and the first inorganic layer;

[0014] wherein the charge passivation layer is disposed between the first organic substrate and the second inorganic layer, and / or the charge passivation layer is disposed between the second organic substrate and the first inorganic layer.

[0015] Optionally, in one embodiment, the charge passivation layer is provided on a side surface of the second organic substrate close to the thin film transistor layer.

[0016] Optionally, in one embodiment, the charge passivation layer is prepared by charge passivation of the same organic material as the first organic substrate, or the charge passivation layer is prepared by charge passivation of the same organic material as the second organic substrate.

[0017] Optionally, in one embodiment, the charge passivation layer is prepared by F passivation of the same organic material as the first organic substrate, or the charge passivation layer is prepared by F passivation of the same organic material as the second organic substrate.

[0018] Optionally, in one embodiment, the first organic substrate and the second organic substrate have the same organic material.

[0019] Optionally, in one embodiment, the charge passivation layer has a dielectric constant of less than or equal to 2.7, and a transmittance of light with a wavelength of 380 nm to 780 nm of more than or equal to 79%.

[0020] Optionally, in one embodiment, the charge passivation layer includes a constitutional element represented by -X-Y-, wherein X includes a first constitutional unit derived from a tetracarboxy dianhydride, Y includes a second constitutional unit derived from a diamine, and at least one of the first constitutional unit and the second constitutional unit includes an electron-withdrawing group.

[0021] The electron-withdrawing group is selected from at least one of a nitro group, a trifluoromethyl group, a trichloromethyl group, a tribromomethyl group, a triiodomethyl group, a cyano group, a sulfonic acid group, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0022] Optionally, in one embodiment, the charge passivation layer further includes a third constitutional unit derived from a tetracarboxy dianhydride and / or a fourth constitutional unit derived from a diamine, a mass percentage of constitutional units including an electron-withdrawing group in the first constitutional unit and the third constitutional unit is 2% to 6% of a mass percentage of the first constitutional unit and the third constitutional unit; and / or

[0023] a mass percentage of constitutional units including an electron-withdrawing group in the second constitutional unit and the fourth constitutional unit is 2% to 6% of a mass percentage of the second constitutional unit and the fourth constitutional unit.

[0024] Optionally, in one embodiment, the material of the charge passivation layer includes a constitutional element represented by any one of the following formulas (1) to (3):

[0025]

[0026] wherein, in formula (1), R1 to R8 are each independently selected from H and a fluorine-containing substituent, and at least one of R1 to R8 is a fluorine-containing substituent;

[0027]

[0028] wherein, in formula (2), R1 to R7 are each independently selected from H and a fluorine-containing substituent, and at least one of R1 to R7 is a fluorine-containing substituent;

[0029]

[0030] wherein, in formula (3), R1 to R4 are each independently selected from H and a fluorine-containing substituent, and at least one of R1 to R4 is a fluorine-containing substituent.

[0031] Optionally, in one embodiment, the material of the charge passivation layer comprises constituent elements represented by any one of the following formulae (4) to (10):

[0032]

[0033] The flexible display panel of the present application forms a charge passivation layer comprising an electron-withdrawing group between the first organic substrate and the thin film transistor, and the charge passivation layer is capable of binding the movement of electrons, thereby preventing the charges generated by the polarization of the first organic substrate from affecting the thin film transistor arranged thereon, maintaining the electrical stability of the thin film transistor, and reducing the occurrence of residual images. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the present application, the drawings required to be used in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to these drawings without any creative labor.

[0035] Figure 1 Schematic diagram of the principle of the existing polyimide affecting the electrical properties of the thin film transistor.

[0036] Figure 2 Schematic diagram of the principle of the existing polyimide forming CTC within the molecule and between the molecules.

[0037] Figure 3 Schematic diagram of the change of the threshold voltage of the thin film transistor arranged on the polyimide and the thin film transistor arranged on the glass at different temperatures and voltages.

[0038] Figure 4 Schematic diagram of the structure of the flexible display panel of the first embodiment of the present application.

[0039] Figure 5 (a) is an EDX (Energy Dispersive X-Ray Spectroscopy) chart of the fluorine-containing polyimide film of Example 1 of the present application, Figure 5 (b) is an element distribution chart of C, O and F of the fluorine-containing polyimide film of Example 1 of the present application.

[0040] Figure 6 (a) is an EDX chart of the polyimide film of the comparative example, Figure 6 (b) is an element distribution chart of C, O and F of the polyimide film of the comparative example.

[0041] Figure 7 is a relationship between dielectric constant and long-time residual image of the polyimides of Examples 1 to 3 and the comparative example.

[0042] Figure 8 is a structure schematic diagram of the flexible display panel of the second embodiment of the present application. DETAILED DESCRIPTION

[0043] The technical solutions in the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0044] In the present application, unless explicitly specified and limited, the first feature is "on" or "under" the second feature, which can include that the first and second features are directly connected, or the first and second features are not directly connected but are connected through another feature between them. Moreover, the first feature "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only means that the first feature is higher than the second feature in horizontal height. The first feature "under", "below" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or only means that the first feature is lower than the second feature in horizontal height. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features with "first", "second" can explicitly or implicitly include one or more features.

[0045] In view of the image sticking problem in the display panel with an organic material as a substrate, the inventors have studied the problem with a polyimide organic substrate as an example. It is found that the polyimide material commonly used by the panel manufacturers is a polyamic acid polymer compound synthesized from 3,3',4,4'-biphenyl tetracarboxylic diandhydride (BPDA) and p-phenylenediamine (p-PDA). This polyimide material generally has good dimensional stability and mechanical properties, but due to the orderly arrangement of the molecular structure and the high molecular packing density, as shown in Figure 1 , the charge transfer complex (CTC) effect is strong within and between the molecules. The electrons within and between the polyimide molecules are transferred, resulting in polarization of the polyimide. As shown in Figure 2 , especially during the fabrication of the array substrate, the polyimide material is polarized, resulting in the accumulation of charges on the surface of the polyimide film PI. When the thin film transistor device TFT disposed on the surface of the polyimide film PI is in operation, the charges accumulated on the surface of the polyimide film PI will affect the characteristics of the transistor device TFT, thereby causing image sticking during the operation of the panel. Please refer to Figure 3 , the inventors measured the threshold voltage (Vth) of the thin film transistor disposed on the polyimide substrate and the thin film transistor disposed on the glass substrate at different temperatures and voltages. The experimental results show that, under the same temperature and voltage stress, the positive drift of the threshold voltage of the thin film transistor disposed on the polyimide substrate is much larger than that of the thin film transistor disposed on the glass substrate. Moreover, after the stress is removed, the threshold voltage quickly returns to the original level, confirming the effect of the polyimide charges on the characteristics of the thin film transistor.

[0046] In order to avoid the effect of polarization of the organic material on the electrical properties of the thin film transistor, the present application provides a flexible display panel, which comprises a first organic substrate, a charge passivation layer, a first inorganic layer, and a thin film transistor layer. The charge passivation layer is disposed on one side of the first organic substrate, and the charge passivation layer comprises an electron-accepting group. The first inorganic layer is disposed on the side of the charge passivation layer away from the first organic substrate. The thin film transistor layer is disposed on the side of the first inorganic layer away from the first organic substrate.

[0047] The flexible display panel of the present application forms a charge passivation layer comprising an electron-accepting group between the first organic substrate and the thin film transistor. The charge passivation layer can bind the movement of electrons, thereby preventing the charges generated by the polarization of the first organic substrate from affecting the thin film transistor disposed thereon, maintaining the electrical stability of the thin film transistor, and reducing the occurrence of image sticking.

[0048] Reference is made to Figure 4 The present application provides a flexible display panel 100. Optionally, the flexible display panel 100 can be an organic light emitting diode display panel. The flexible display panel 100 comprises a substrate 10, a first inorganic layer 20, and a thin film transistor layer 30. The first inorganic layer 20 is disposed on one side of the substrate 10, and the thin film transistor layer 30 is disposed on a side of the first inorganic layer 20 away from the substrate 10.

[0049] The substrate 10 comprises a first organic substrate 11, a second organic substrate 12, and a second inorganic layer 13 disposed between the first organic substrate 11 and the second organic substrate 12. The second inorganic layer 13 is disposed between the first organic substrate 11 and the first inorganic layer 20. The second organic substrate 12 is disposed between the second inorganic layer 13 and the first inorganic layer 20. The first organic substrate 11 and the second organic substrate 12 can have the same organic material. It should be noted that in the present embodiment, the organic substrate of the substrate 10 away from the thin film transistor layer 30 is referred to as the first organic substrate 11, and the organic substrate close to the thin film transistor layer 30 is referred to as the second organic substrate 12. In other embodiments of the present application, the first organic substrate 11 can also be the organic substrate close to the thin film transistor layer 30, and the second organic substrate 12 can also be the organic substrate away from the thin film transistor layer 30.

[0050] Optionally, the first inorganic layer 20 comprises at least one of a buffer layer BL and a barrier layer 3L. In the present embodiment, the first inorganic layer 20 comprises the buffer layer BL and the barrier layer 3L. The buffer layer BL comprises silicon nitride, silicon oxide, or a stack of silicon nitride and silicon oxide. The barrier layer 3L comprises a stack of silicon nitride, silicon oxide, and a-Si.

[0051] The flexible display panel 100 further comprises a charge passivation layer 14 disposed on a side of the first organic substrate 11 close to the thin film transistor layer 30. The charge passivation layer 14 comprises an electron-accepting group. Optionally, the charge passivation layer 14 is disposed between the first organic substrate 11 and the second inorganic layer 13, and / or the charge passivation layer 14 is disposed between the second organic substrate 12 and the first inorganic layer 20. Further, the charge passivation layer 14 is disposed on a surface of the first organic substrate 11 close to the thin film transistor layer 30, and / or the charge passivation layer 14 can also be disposed on a surface of the second organic substrate 12 close to the thin film transistor layer 30.

[0052] The charge passivation layer 14 is located between the organic substrate and the thin film transistor layer 30, which can prevent the material polarization of the organic substrate from affecting the operation of the thin film transistor layer 30. Further, an inorganic layer is also disposed between the charge passivation layer 14 and the thin film transistor layer 30, which can prevent water vapor from the charge passivation layer 14 from invading.

[0053] Optionally, the charge passivation layer 14 is prepared by charge passivation of the same organic material as the first organic substrate 11, or the charge passivation layer 14 is prepared by charge passivation of the same organic material as the second organic substrate 12. Further, the charge passivation layer 14 is prepared by F-ization of the same organic material as the first organic substrate 11, or the charge passivation layer 14 is prepared by F-ization of the same organic material as the second organic substrate 12.

[0054] Specifically, the charge passivation layer 14 can include a first charge passivation layer 141 and a second charge passivation layer 142. The first charge passivation layer 141 is disposed between the first organic substrate 11 and the thin film transistor layer 30. Further, the first charge passivation layer 141 is disposed on the side surface of the first organic substrate 11 close to the thin film transistor layer 30. The second charge passivation layer 142 is disposed between the second organic substrate 12 and the thin film transistor layer 30. Further, the second charge passivation layer 142 is disposed on the side surface of the second organic substrate 12 close to the thin film transistor layer 30. Optionally, the thickness of the first organic substrate 11 is 5 to 15 microns, and the thickness of the second organic substrate 12 is 5 to 10 microns.

[0055] Hereinafter, the material of the first organic substrate 11 and the first charge passivation layer 141 will be described in detail. The second organic substrate 12 and the second charge passivation layer 142 can refer to the first organic substrate 11 and the first charge passivation layer 141.

[0056] The first charge passivation layer 141 is prepared by charge passivation of the same organic material as the first organic substrate 11. Specifically, the first charge passivation layer 141 is prepared by F-ization of the same organic material as the first organic substrate 11. It can be understood that the first charge passivation layer 141 can also be prepared by charge passivation of the same organic material as the second organic substrate 12. Conversely, the second charge passivation layer 142 can also be prepared by charge passivation of the same organic material as the first organic substrate 11.

[0057] The material of the first organic substrate 11 is a conventional polyimide. The material of the first charge-impedance layer 141 is a polyimide containing an electron- withdrawing group. The electron-withdrawing group contained in the first charge-impedance layer 141 is capable of trapping electrons, binding the movement of electrons, thereby functioning as a charge-impedance. Optionally, the electron-withdrawing group can be selected from at least one of a nitro group, a trifluoromethyl group, a trichloromethyl group, a tribromomethyl group, a triiodomethyl group, a cyano group, a sulfonic acid group, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Note that the material of the first organic substrate 11 can also be one of polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyarylate (PAR), polycarbonate (PC), polyetherimide (PEI), and polyethersulfone (PES). In this case, the material of the first charge-impedance layer 141 is the above-described material containing an electron-withdrawing group.

[0058] Optionally, the first charge-impedance layer 141 of the polyimide containing an electron-withdrawing group can be formed by utilizing a condensation reaction of a tetracarboxylic dianhydride and a diamine, wherein at least one of the tetracarboxylic dianhydride and the diamine contains an electron-withdrawing group, or mixing the tetracarboxylic dianhydride, the diamine, and an alcohol containing an electron-withdrawing group, and forming a substituent of the electron-withdrawing group on the tetracarboxylic dianhydride or the diamine at the same time of the condensation reaction. Specifically, the material of the first charge-impedance layer 141 includes a constitutional element represented by -X-Y-, wherein X represents a constitutional unit derived from the tetracarboxylic dianhydride, and Y represents a constitutional unit derived from the diamine. X contains a first constitutional unit derived from the tetracarboxylic dianhydride, Y contains a second constitutional unit derived from the diamine, and at least one of the first constitutional unit and the second constitutional unit contains an electron-withdrawing group.

[0059] The tetracarboxylic dianhydride can be selected from tetracarboxylic dianhydrides represented by formulae (X1) to (X7):

[0060]

[0061] The diamine can be selected from diamines represented by formulae (Y1) to (Y3):

[0062]

[0063] Note that the above-described dianhydride or diamine represented by (X1) to (X7) and (Y) to (Y3) is exemplified by an electron-withdrawing group containing fluorine, and the dianhydride or diamine of the present application is not limited to the above-described ones.

[0064] The fluorine-containing electron-withdrawing group has poor thermal stability, and is enriched at the interface during curing, forms a hydrogen bond with OH- and other groups, and thus forms a first charge passivation layer 141 on the surface. Further, the addition of the electron-withdrawing group can affect the thermal stability of the polyimide. Therefore, in addition to the electron-withdrawing group-containing constituent unit derived from tetracarboxy dianhydride and the electron-withdrawing group-containing constituent unit derived from diamine in the first charge passivation layer 141, non-electron-withdrawing group-containing constituent units derived from tetracarboxy dianhydride and non-electron-withdrawing group-containing constituent units derived from diamine, or commonly used constituent units derived from tetracarboxy dianhydride and diamine in the art, can also be included to ensure the thermal stability of the polyimide. Specifically, the first charge passivation layer 141 further comprises a third constituent unit derived from tetracarboxy dianhydride and / or a fourth constituent unit derived from diamine. Among them, the mass percentage of the electron-withdrawing group-containing constituent unit in the first constituent unit and the third constituent unit accounts for 2% to 6%, preferably 3% to 6% of the mass percentage of the first constituent unit and the third constituent unit; and / or the mass percentage of the electron-withdrawing group-containing constituent unit in the second constituent unit and the fourth constituent unit accounts for 2% to 6%, preferably 3% to 6% of the mass percentage of the second constituent unit and the fourth constituent unit. When the mass percentage of the electron-withdrawing group-containing constituent unit in the first constituent unit to the fourth constituent unit exceeds 6%, outgassing may be caused, affecting the thermal stability, and when the mass percentage of the electron-withdrawing group-containing constituent unit in the first constituent unit to the fourth constituent unit is less than 2%, the passivation of electrons is not obvious.

[0065] In the following, several different cases are described in detail.

[0066] In an embodiment, the first charge passivation layer 141 comprises polyimide constituent elements represented by the following formula:

[0067] -Ya-Xa-Ya-, -Ya-Xb-Ya-, wherein Xa is a first constituent unit derived from tetracarboxy dianhydride without an electron-withdrawing group, Xb is a third constituent unit derived from tetracarboxy dianhydride commonly used in the art with an electron-withdrawing group, and Ya represents a second constituent unit derived from diamine without an electron-withdrawing group. Among them, the mass percentage of Xb accounts for 2% to 6% of the total mass percentage of Xa and Xb.

[0068] In an embodiment, the first charge passivation layer 141 comprises polyimide constituent elements represented by the following formula:

[0069] -Ya-Xa-Ya-, -Yb-Xa-Yb-, -Ya-Xa-Yb-, where Xa is the first constituent unit derived from tetracarboxylic dianhydride without electron-withdrawing groups, Ya represents the second constituent unit derived from diamine without electron-withdrawing groups, and Yb represents the fourth constituent unit derived from diamine containing electron-withdrawing groups. The mass percentage of Yb is 2% to 6% of the total mass percentage of Ya and Yb.

[0070] In one embodiment, the first charge passivation layer 141 comprises polyimide constituent elements represented by the following formula:

[0071] -Ya-Xa-Ya-, -Ya-Xb-Ya-, -Yb-Xa-Yb-, -Yb-Xb-Yb-, -Ya-Xa-Yb-, where Xa is a first constituent unit derived from tetracarboxylic dianhydride without electron-withdrawing groups, Xb is a third constituent unit derived from tetracarboxylic dianhydride containing electron-withdrawing groups, Ya represents a second constituent unit derived from diamine without electron-withdrawing groups, and Yb represents a fourth constituent unit derived from diamine containing electron-withdrawing groups. The mass percentage of Xb is 2% to 6% of the total mass percentage of Xa and Xb, and the mass percentage of Yb is 2% to 6% of the total mass percentage of Ya and Yb, so that the mass percentage of the constituent unit containing electron-withdrawing groups is 2% to 6% of the mass percentage of the first to fourth constituent units.

[0072] Optionally, the first charge passivation layer 141 can also be separately disposed on the first organic substrate 11, that is, the first organic substrate 11 is formed first, and then the first charge passivation layer 141 is formed on the first organic substrate 11. It should be noted that as long as the first charge passivation layer 141 can be formed on the surface of the first organic substrate 11, this application does not limit the formation method of the first charge passivation layer 141. The first charge passivation layer 141 of this application can also be a material other than polyimide containing electron-withdrawing groups.

[0073] Optionally, the material of the first charge passivation layer 141 comprises any of the constituent elements represented by formulas (1) to (3):

[0074]

[0075] In formula (1), R1 to R8 are independently selected from H and fluorinated substituents, and at least one of R1 to R8 is a fluorinated substituent;

[0076]

[0077] In formula (2), R1 to R7 are independently selected from H and fluorinated substituents, and at least one of R1 to R7 is a fluorinated substituent;

[0078]

[0079] wherein, in formula (3), R1 to R4 are each independently selected from H and a fluorine-containing substituent, and at least one of R1 to R4 is a fluorine-containing substituent.

[0080] Specifically, the fluorine-containing substituent can be a fluorine atom or a trifluoromethyl group.

[0081] During the curing process of the fluorine-containing polyimide, fluorine atoms will spontaneously migrate and gather on the surface layer of the polyimide. The principle of weakening the intramolecular and intermolecular CTC is that the introduction of fluorine and other strong electron-withdrawing groups in the molecule leads to the weakening of the intramolecular and intermolecular electron delocalization, which is captured by the fluorine atom. The intermolecular and intermolecular delocalization effect is weakened, preventing the polarization of the polyimide. Further, when the fluorine-containing substituent is a trifluoromethyl group, the trifluoromethyl group is a three-dimensional spatial configuration, which increases the steric hindrance and weakens the intermolecular delocalization effect, further preventing the polarization of the polyimide. When the thin film transistor device provided on the substrate 10 is in operation, the electric field acting on the interface between the polyimide substrate and the thin film transistor device will not cause the free movement of electrons in the polyimide, thereby effectively improving the polarization motion of the traditional polyimide material under the action of the electric field, thereby reducing the influence of the polyimide substrate on the threshold voltage of the thin film transistor, and achieving the effect of improving the long-time residual image.

[0082] More specifically, the material of the first charge passivation layer 141 includes constituent elements represented by any one of the following formulas (4) to (10):

[0083]

[0084] The material of the first charge passivation layer 141 including constituent elements represented by any one of the following formulas (4) to (10) can be easily synthesized by commercially available materials.

[0085] It should be noted that the polyimide including constituent elements represented by formula (7) is a porous 6FXDA / 6FDAm polyimide substrate nanofoam with a nanometer size range.

[0086] Optionally, the first charge passivation layer 141 is integrated with the first organic substrate 11. The first charge passivation layer 141 and the first organic substrate 11 can be manufactured in the same process, thereby simplifying the process and improving the bonding force of the first charge passivation layer 141 and the first organic substrate 11. Of course, the first charge passivation layer 141 and the first organic substrate 11 can also be separate and manufactured by different processes.

[0087] Hereinafter, the preparation method and advantages of the polyimide substrate of the first embodiment of the present application will be described.

[0088] One of the methods of manufacturing the polyimide substrate of the present application is to form a polyimide film having a charge passivation layer of fluorinated polyimide on the surface, and the preparation method thereof includes the following three methods.

[0089] 1) During the synthesis of tetracarboxy dianhydride and diamine monomers, a fluorine-containing diamine monomer is introduced, but the relative content of the fluorine-containing diamine monomer (the mass percentage of the fluorine-containing diamine monomer accounts for the mass percentage of the fluorine-containing diamine monomer and the diamine monomer not containing fluorine) is controlled to be not more than 6%, to form a fluorine-containing polyamic acid, and to form a polyimide by imidization.

[0090] 2) During the synthesis of tetracarboxy dianhydride and diamine monomers, a fluorine-containing tetracarboxy dianhydride monomer is introduced, but the relative content of the fluorine-containing tetracarboxy dianhydride monomer (the mass percentage of the fluorine-containing tetracarboxy dianhydride monomer accounts for the mass percentage of the fluorine-containing tetracarboxy dianhydride monomer and the tetracarboxy dianhydride monomer not containing fluorine) is controlled to be not more than 6%, to form a fluorine-containing polyamic acid, and to form a polyimide by imidization.

[0091] 3) During the synthesis of dianhydride and diamine monomers by stirring reaction, a fluorine-containing small molecule is introduced to form a fluorine-containing polyamic acid, and to form a polyimide by imidization.

[0092] The way of forming a polyimide from a polyamic acid by imidization is: the wet film coating of the polyamic acid is carried out by the way of coating, after the completion of the wet film coating, HVCD (rapid vacuum drying) is carried out to remove the solvent, so that the wet film is shaped, and then high temperature curing is carried out to form a fluorinated polyimide film. Among them, the condition of HVCD is 40 to 80℃, the bottom pressure is 0 to 10Pa, and the time is 250 to 550s. The curing temperature is 400 to 450℃, and the curing time is 13min.

[0093] Example 1

[0094] Biphenyl tetracarboxylic dianhydride, 4,4'-diamino diphenyl ether, and 1-trifluoromethyl-p-phenylenediamine are dissolved in N-methyl pyrrolidone (NMP) in a molar ratio of 100:98:2 to carry out stirring reaction, to generate polyamic acid, and then to make the polyamic acid imidize to form a polyimide film, and to test the performance of the polyimide film. The reaction formula of forming the polyimide film is as follows:

[0095]

[0096] The synthesized polyimide film is used as a substrate 10. As described above, the substrate 10 includes a first organic substrate 11 and a second organic substrate 12. The thickness of the first organic substrate 11 is 5 to 15 microns, and the thickness of the second organic substrate 12 is 5 to 10 microns.

[0097] A layer of SiOx layer was deposited on the substrate 10, and then the thin film transistor layer 30 was fabricated thereon, and the long-term image sticking was measured. The measurement condition of the long-term image sticking was that the initial Just Notice Diffidences (JND) value was measured after the checkerboard pattern was lighted for 10 minutes.

[0098] In addition, EDX scanning and EDX area scanning were performed on the first organic substrate 11 of Example 1.

[0099] Example 2

[0100] Biphenyl tetracarboxylic dianhydride, 2,2'-difluoromethyl-4,4',5,5'-biphenyl tetracarboxylic dianhydride, 4,4'-oxydianiline, and fluoroethanol were dissolved in N-methylpyrrolidone in a molar ratio of 100:100:6, and stirred to react, to thereby produce polyamic acid. The polyamic acid was imidized to form a polyimide film, and the performance of the polyimide film was tested. The reaction formula for forming the polyimide film is shown below.

[0101]

[0102] The substrate 10 was formed using the synthesized polyimide film. As described above, the substrate 10 includes the first organic substrate 11 and the second organic substrate 12. The thickness of the first organic substrate 11 was 5 to 15 micrometers, and the thickness of the second organic substrate 12 was 5 to 10 micrometers.

[0103] A layer of SiOx layer was deposited on the substrate 10, and then the thin film transistor layer 30 was fabricated thereon, and the long-term image sticking was measured. The measurement condition of the long-term image sticking was that the initial Just Notice Diffidences (JND) value was measured after the checkerboard pattern was lighted for 10 minutes.

[0104] Example 3

[0105] Biphenyl tetracarboxylic dianhydride, 4,4'-oxydianiline, and fluoroethanol were dissolved in N-methylpyrrolidone in a molar ratio of 100:100:6, and stirred to react, to thereby produce polyamic acid. The polyamic acid was imidized to form a polyimide film, and the performance of the polyimide film was tested. The reaction formula for forming the polyimide film is shown below.

[0106]

[0107] The substrate 10 was formed using the synthesized polyimide film. As described above, the substrate 10 includes the first organic substrate 11 and the second organic substrate 12. The thickness of the first organic substrate 11 was 5 to 15 micrometers, and the thickness of the second organic substrate 12 was 5 to 10 micrometers.

[0108] A layer of SiOx layer was deposited on the substrate 10, followed by the fabrication of thin film transistor layer 30 thereon, and the long-time residual image was measured. The measurement condition of long-time residual image was that after the chessboard grid was lighted for 10 minutes, the initial perceptible difference was measured.

[0109] Comparative Example

[0110] A polyimide film was synthesized by a conventional method to form a substrate. As described above, the substrate included two polyimide substrates. The thickness of the polyimide substrate away from the thin film transistor was 5 to 15 micrometers, and the thickness of the polyimide substrate close to the thin film transistor was 5 to 10 micrometers.

[0111] A layer of SiOx layer was deposited on the substrate 10, followed by the fabrication of thin film transistor layer 30 thereon, and the long-time residual image was measured. The measurement condition of long-time residual image was that after the chessboard grid was lighted for 10 minutes, the initial perceptible difference was measured.

[0112] In addition, EDX surface scanning was also performed on the polyimide substrate away from the thin film transistor of the comparative example.

[0113] Referring to Figure 5 (a) of FIG. 1, Figure 5 (a) of FIG. 1 shows that the fluorine-containing polyimide of Example 1 was successfully synthesized, Figure 5 the brighter part in the third graph of (b) of FIG. 1 shows the content and distribution of fluorine atoms in the first polyimide substrate. Referring to Figure 6 (a) of FIG. 1, Figure 6 (a) of FIG. 1 shows that the polyimide in the comparative example does not contain fluorine, Figure 6 (b) of FIG. 1 shows that there are no fluorine atoms in the polyimide substrate.

[0114] The performance data of Examples 1 to 3 and the comparative example are as follows.

[0115] Table 1 Performance data of polyimide of Examples 1 to 3

[0116]

[0117] As can be seen from Table 1, the characteristics of the fluorinated polyimide material did not change significantly compared with conventional polyimide. The dielectric constant of the polyimide film of Examples 1 to 3 was reduced and was less than or equal to 2.7. Moreover, as the content of F atoms increased, the dielectric constant of the fluorinated polyimide film gradually decreased. The transmittance of the polyimide film of Examples 1 to 3 to light of 380 to 780 nanometers was greater than or equal to 79%, which was slightly improved compared with existing polyimide, and was more conducive to being used as a substrate material for under-screen camera OLED backplanes.

[0118] Referring to Figure 7The fluorinated polyimide film used as the substrate of the array substrate structure in Embodiments 1 to 3 can effectively improve the problem of long-time residual image caused by the large drift of threshold voltage of the thin film transistor device during operation when the conventional polyimide material is used as the substrate of the array substrate. The dielectric constant of the fluorinated polyimide is small due to the presence of the electron-withdrawing group such as fluorine. The polarization ability of the polyimide is weak under the stress of voltage and temperature. Even if the polyimide is polarized, the separation of charges is slow. The threshold voltage of the thin film transistor device drifts slowly under the stress of voltage and temperature, and recovers slowly. Thus, the long-time residual image is effectively improved.

[0119] In the above-described embodiments, the use of the double-layered polyimide substrate containing the electron-withdrawing group as the substrate of the charge passivation layer is exemplified, and the ability to bind electrons is stronger. It can be understood that in other embodiments of the present application, it is only necessary that at least one of the first organic substrate 11 and the second organic substrate 12 is provided with the charge passivation layer near the surface of the thin film transistor layer 30.

[0120] Optionally, the substrate 10 of the present application can also include a single-layered polyimide substrate and a layer of charge passivation layer. The thickness of the single-layered polyimide substrate is 15 microns or 12 microns.

[0121] Please refer to Figure 8 The second embodiment of the present application is different from the first embodiment in that:

[0122] The first inorganic layer 20 is a barrier layer. The barrier layer includes a stack of silicon nitride, silicon oxide, and a-Si. The charge passivation layer 24 is disposed between the buffer layer BL and the first inorganic layer 20.

[0123] In the second embodiment of the present application, by disposing the charge passivation layer between the barrier layer and the thin film transistor, the effect of binding the movement of electrons and reducing the influence of the polarization of the organic substrate on the thin film transistor can also be achieved.

[0124] As a variant of the present application, the buffer layer BL includes silicon nitride, silicon oxide, or a stack of silicon nitride and silicon oxide. The barrier layer includes a stack of silicon nitride, silicon oxide, and a-Si. Each layer of the buffer layer BL and the barrier layer 3L can be referred to as the first inorganic layer 20. The flexible display panel 100 can include at least one charge passivation layer 24 disposed between the first inorganic layer 20 and the thin film transistor layer 30. That is, the charge passivation layer 24 can be disposed outside the buffer layer BL and the barrier layer 3L, or inside the buffer layer BL and the barrier layer 3L.

[0125] The above provides a detailed description of the embodiments of the present application, and the principles and embodiments of the present application are described by applying specific examples. The above description of the embodiments is only used to help understand the present application. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific embodiments and application scope will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1.A flexible display panel, characterized in that, Comprising: a first organic substrate; a charge passivation layer disposed on one side of the first organic substrate, the charge passivation layer including an electron-withdrawing group; a first inorganic layer disposed on a side of the charge passivation layer distal from the first organic substrate; a thin film transistor layer disposed on a side of the first inorganic layer distal from the first organic substrate; wherein the charge passivation layer includes an electron-withdrawing group-containing constituent unit derived from a tetracarboxy dianhydride, an electron-withdrawing group-containing constituent unit derived from a diamine, an electron-withdrawing group-free constituent unit derived from a tetracarboxy dianhydride, and an electron-withdrawing group-free constituent unit derived from a diamine. 2.The flexible display panel of claim 1, wherein, The charge passivation layer is disposed on a side surface of the first organic substrate proximal to the thin film transistor layer. 3.The flexible display panel of claim 1, wherein, Further comprising: a second inorganic layer disposed between the first organic substrate and the first inorganic layer; a second organic substrate disposed between the second inorganic layer and the first inorganic layer; wherein the charge passivation layer is disposed between the first organic substrate and the second inorganic layer, and / or the charge passivation layer is disposed between the second organic substrate and the first inorganic layer. 4.The flexible display panel of claim 3, wherein, The charge passivation layer is disposed on a side surface of the second organic substrate proximal to the thin film transistor layer. 5.The flexible display panel of claim 3, wherein, The charge passivation layer is prepared using the same organic material as the first organic substrate, or the charge passivation layer is prepared using the same organic material as the second organic substrate. 6.The flexible display panel of claim 5, wherein, The charge passivation layer is prepared using the same organic material as the first organic substrate, or the charge passivation layer is prepared using the same organic material as the second organic substrate. 7.The flexible display panel of claim 5, wherein, The first organic substrate and the second organic substrate have the same organic material. 8.The flexible display panel of claim 5, wherein, The charge passivation layer has a dielectric constant of less than or equal to 2.7, and a transmittance of greater than or equal to 79% for light having a wavelength of 380 nm to 780 nm. 9.The flexible display panel of claim 1, wherein, The charge passivation layer includes a constituent element represented by -X-Y-, wherein X includes a first constituent unit derived from a tetracarboxy dianhydride, Y includes a second constituent unit derived from a diamine, and at least one of the first constituent unit and the second constituent unit includes an electron-withdrawing group; The electron-withdrawing group is selected from at least one of a nitro group, a trifluoromethyl group, a trichloromethyl group, a tribromomethyl group, a triiodomethyl group, a cyano group, a sulfonic acid group, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. 10.The flexible display panel of claim 9, wherein, The charge passivation layer further includes a third constituent unit derived from a tetracarboxy dianhydride and / or a fourth constituent unit derived from a diamine, a mass percentage of electron-withdrawing group-containing constituent units in the first constituent unit and the third constituent unit is 2% to 6% of a mass percentage of the first constituent unit and the third constituent unit; and / or a mass percentage of electron-withdrawing group-containing constituent units in the second constituent unit and the fourth constituent unit is 2% to 6% of a mass percentage of the second constituent unit and the fourth constituent unit. 11.The flexible display panel of claim 10, wherein, The material of the charge passivation layer includes a constituent element represented by any one of the following formulas (1) to (3): wherein, in formula (1), R1to R8are each independently selected from H and a fluorine-containing substituent, and at least one of R1to R8is a fluorine-containing substituent; wherein, in formula (2), R1to R7are each independently selected from H and a fluorine-containing substituent, and at least one of R1to R7is a fluorine-containing substituent; wherein, in formula (3), R1to R4are each independently selected from H and a fluorine-containing substituent, and at least one of R1to R4is a fluorine-containing substituent. 12.The flexible display panel of claim 11, wherein, The material of the charge passivation layer includes constituent elements represented by any one of the following formulas (4) to (10):

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